Why so many unintended side effects with genetic engineering?

It would help activists enormously if they could access the precise ways in which genetic engineering leads to unintended side effects. There are many ways this can happen. I have organized some in the following points:

1) the gene inserted into a host DNA can jump out of it more easily and become incorporated into the DNA of other organisms, such as gut bacteria, soil microorganisms, and possibly even somatic cells. This tendency to jump is a result of two factors: 1) the host DNA has defense mechanisms that prevent foreign DNA from entering into it and 2) the inserted gene is usually attached to segments of viral DNA that it uses to force open the code DNA (just as viruses are able to do this!). These viral segments make the inserted genes unstable and more likely to migrate out -but also more likely to force themselves into some other DNA as well (see Ho, 2000, for details).

2) the gene inserted into a host DNA will behave unpredictably because it will interact with the other genes and regulatory mechanisms within the host code. DNA codes form genetic networks where different genes regulate each other's expression. DNA coding is NOT a one-to-one mapping (google "pleiotropic effects" if you don't believe me!). It is full of feedback loops and recursions!

3) similarly, when we insert a gene into a host DNA, the host genes will behave unpredictably because of the novel gene now expressing itself in the genetic network. Because of points 2 and 3, it is best to consider the DNA code ecologically, where the function of genetic segments depend on relational factors and are not pre-set and determinate.

4) if the organism manages to survive to adulthood (and this is unlikely: of the thousands of successfully inserted genes into host codes, the majority die during development or infancy because of mutations that arise from the new gene interacting deleteriously with its neighbors) it will have novel behaviors, physiology, and biochemistry. Because of this, it will interact unpredictably with other organisms in its ecological communities.

5) some genetic effects do not show immediately but rather appear during stressful or limiting situations in the organism's life, when "epigenetic factors" cause genes to switch on or off at different rates and in different patterns. Similarly, some genetic effects will only show in future generations, as new environmental factors elicit new patterns of genetic expression (a great description of the relationship between genetic and epigenetic factors can be read in Jablonka & Lamb, 2006).